In hybrid vehicles two or more drive units are combined with one another, which, in different manners, provide the power required for operating the vehicle. Due to the fact that the features of an internal combustion engine and an electric motor complement one another in a particularly beneficial manner, presently common hybrid vehicles are mostly provided with a combination of an internal combustion engine and an electric motor. The operation of the vehicle via the electric motor occurs primarily in the range of small loads, because the internal combustion engine provides considerably lower levels of effectiveness under partial load than under full load. Under higher loads the operation occurs preferably via the internal combustion engine, because then the electric energy accumulator, from which the electric motor is supplied during operation, can be recharged with relatively good effectiveness by an additional generating operation of the electric motor. Furthermore, in order to increase the maximum torque provided for the vehicle, the release of momentum by the internal combustion engine and the electric motor can additionally occur parallel.
In multi-cylinder internal combustion engines, higher overall effectiveness can be achieved by switching off some cylinders, because the remaining cylinders can be operated with higher effectiveness. A hybrid drive with a thermal engine is known from DE 100 06 743 A1, for example, which is provided with the possibility to switch off cylinders in order to avoid any operation under partial load.
A purely electric drive using the electric motor is only useful in combination with a conventional internal combustion engine when the internal combustion engine and the electric motor can be uncoupled mechanically. Otherwise, the drag momentum to be provided for the internal combustion engine switched off leads to a large portion of the electric energy having to be provided for this purpose. In particular, in the lower load range only very low overall effectiveness can be achieved in such a mode of operation. A mechanical uncoupling of the internal combustion engine from the electric motor, for example by an additional clutch, involves an increased construction expense and, thus, considerably increased costs. Furthermore, high expenses result for an adjustment of the overall system for the purpose of comfort, because the uncoupling and, in particular, the coupling of the internal combustion engine to the electric motor, even in dynamic drive situations, must be performed to the extent possible without any leaps in momentum and/or any vehicle jerks resulting therefrom. An alternative for a mechanical uncoupling is the reduction of the drag momentum by way of deactivating a valve operation of cylinders that are switched off.
In addition to concepts, in which merely the fuel supply for the cylinders that are switched off is interrupted, it is known to switch them off by controlling the inlet and outlet valves. For example, from DE 102 04 129 a hybrid vehicle is known, in which, for the purpose of switching off the internal combustion engine causing little vibrations, in addition to reducing the fuel supply, the release of condensing means is initiated, in particular in a piston. The release of the condensing means can be achieved by opening a throttle, shortening a compression phase, shortening the time, at which both the inlet and the outlet valves are simultaneously closed, a permanent opening of the inlet and outlet valves or the like. Additionally, one or more cylinders of the internal combustion engine can be switched off mechanically. This can be achieved such that a cylinder control addresses the inlet and outlet valve, either directly or indirectly or via a control for the camshaft such, that the outlet and the inlet valve of the combustion chamber are permanently opened or closed when the internal combustion engine is switched off.
From DE 42 92 543 C1 a motor control method has been known for a suction pipe injection engine, in which immediately prior deactivation air only is suctioned into the cylinders that can be switched off and thus it is prevented that exhaust can be enclosed in the cylinders. When actuating a cylinder previously switched off the valve drives, which are allocated to the cylinders switched off, are released from the interruption of the valve operation, i.e. are reactivated. Further, by means of a detection device it is determined if or if not the motor is operating in a core range for rapid acceleration. If the motor is operating in a core range for rapid acceleration, a preliminary, i.e. preparatory fuel injection occurs in the cylinders that can be switched off. In normal conditions, the fuel injection is initiated after the valve operation has begun, i.e. after air only had been suctioned into the cylinders that can be switched off. Based on the effects of films forming on the wall of the manifold passage during indirect fuel injection, an additional amount of fuel mass, which is hard to determine, is located in the cylinder that previously had been switched off, leading to a high level of inaccuracy in the admeasurement of the correct fuel amount for the requested targeted air ratio at activation. Additionally, a small amount of fuel and oil will reach the cylinder combustion chamber via blow-by, depending on the duration of the switch off-phase, and thus leading to an additional modification of the composition of the mixture.
Further, from DE 195 46 549 C1 it is known to add a cylinder after the suction cycle and prior to the outlet cycle. In order to avoid an undesired cooling of the combustion chamber it is suggested to keep the hot exhaust gas in the cylinders switched off during the switch off-phase.
In order to prevent an undesired momentum jerk during the deactivation and/or activation of cylinders, in EP 1 298 300 A2 it is suggested, prior to deactivation, to reduce the power of the cylinders to be switched off during partial motor operation and simultaneously to increase the power of the cylinders that continue operating. When the cylinders are reactivated their power is increased, while the power of the cylinders that continue to operate is reduced or maintained constant. Due to the fact that loss of gas can occur by leaks in a cylinder that has been switched off, it is suggested in DE 33 16 446 A1 to briefly open the inlet valve even in cylinders that have been switched off.